High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 × 10 −6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys with optimal thermal, magnetic, and electrical properties.

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MAX phases that exhibit long-range magnetic order in the bulk are still very hard to synthesize. Chromium and manganese are the cutoff elements when transitioning through the 3dmetals that still form stable full and doped MAX phases, respectively. An iron-based (on the M-site) bulk MAX phase does not exist. Therefore, other strategies to induce long-range magnetic ordering in bulk MAX phases are necessary to open the path to new functional materials. Here, we demonstrate the nonconventional synthesis of a hitherto unknown MAX phase solid-solution (V1–x Cr x )2GaC by microwave heating. The full series with 0 < x < 1 (x = 0.20, 0.40, 0.50, 0.60, 0.80) forms almost single phase with minimal differences in their morphology. Their magnetic properties, however, differ rather significantly, with a maximum susceptibility around x = 0.80. Both the experimental and theoretical/ab initio magnetic analysis confirm that the solid-solution (V1–x Cr x )2GaC is an itinerant Pauli paramagnet that almost fulfills the Stoner criterion for ferromagnetic order (for compositions with x around 0.80). This is a powerful insight into how chemical composition couples with electronic structure and the resulting bulk magnetic properties because it provides crucial guidelines to produce long-range ordered magnetic MAX phases.

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Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of c-axis-oriented Sm2Co17 and SmCo5 phases is stabilized. While typically in the prototype Sm­(Co, Fe, Cu, Zr)7.5–8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm–Co system is shown. A detailed analysis of the extended X-ray absorption fine structure confirmed the coexistence of Sm2Co17 and SmCo5 phases with 65% Sm2Co17 and 35% SmCo5. The SmCo5 phase is stabilized directly on an Al2O3 substrate up to a thickness of 4 nm followed by a matrix of Sm2Co17 intermixed with SmCo5. This structural transition takes place through coherent atomic layers, as revealed by scanning transmission electron microscopy. Highly crystalline growth of well-aligned Sm2Co17 and SmCo5 phases with coherent interfaces result in strong exchange interaction, leading to enhanced magnetization and magnetic coupling. The arrangement of Sm2Co17 and SmCo5 phases at the nanoscale is reflected in the observed magnetocrystalline anisotropy and coercivity. As next-generation permanent magnets require designing of materials at an atomic level, this work enhances our understanding of self-assembling and functioning of nanophased magnets and contributes to establishing new concepts to engineer the microstructure for beyond state-of-the-art magnets.